Because of chemical inertness, low allergenic properties, high tensile strength and low melting point, polyolefin fiber and filaments, such as polypropylene are favored candidates for producing a variety of commercial products, particularly nonwoven products used in intimate contact with the human body.
In attempting to apply existing technology and material to meet competitive marketing needs, however, it is sometimes found that the cost and technical problems which arise far exceed the marketing advantages gained.
By way of example, nonwoven material used as cover sheets for diapers, sanitary napkins, and the like, must be cost competitive and retain substantial cross directional (CD) strength and energy (toughness) as well as the usual surface softness, short liquid strike through time, and limited rewetting properties.
Unfortunately, however, softness, absorbency, CD strength and the like are generally not compatible characteristics among synthetic nonwoven materials.
In particular, softness is usually gained in such material at the expense of lowered cross directional (CD) strength, and at a substantial increase in cost, figured on a Spun Weight/Time basis.
While the cross directional strength of such materials can usually be increased by increasing the bonding area and/or number of bonding loci, this is effected at the expense of necessary softness, feel, strike through and rewet properties.
In effect, therefore, the resulting nonwoven product represent a deliberate compromise, in which particular desirable characteristics are maximized and certain undesirable characteristics minimized, if possible, and accepted in exchange.
In the case of personal contact products such as diaper cover stock and the like, it is also found desirable to satisfy certain non-functional esthetic properties, such as increased opacity (preferably 32%-45%) and stain-masking ability to enhance marketability. In order to accomplish such further improvement, however, the difficulty in obtaining an acceptable compromise is greatly increased.
Generally, staining and opacity problems in synthetic nonwovens have been catagorized and treated in the art as unresolved coloring problems, which have been greatly complicated by the chemically inert nature of polyolefins such as polypropylene. For this reason colorants and brighteners are preferably introduced as spun melt components. This, in turn, has raised additional problems with respect to leaching, allergenic properties, CD strength loss, smaller spin quench windows, increased cost and the like.
It is an object of the present invention to increase the opacity of polyolefin-containing nonwoven material obtained from at least one web, without raising such added problems.
It is also an object of the present invention to minimize or avoid the need for high concentrations of colorants in nonwoven cover stock material to increase the opacity thereof.